This project will utilize murine monoclonal antibodies directed toward human IgG as well as specific monoclonal antibodies to the individual IgG subclasses to explore the relationship of IgG subclass type and amount in the immune destruction of red cells and platelets in patients with autoimmune hemolytic anemia and immune thrombocytopenic purpura. This will be carried out in two major research efforts. In the first, red cells and platelets from patients with autoimmune hemolytic anemia and immune thrombocytopenic purpura will be isolated and the type and quantity of IgG immunoglobulin subclass determined on the cell surfaces and correlated with the extent of anemia or thrombocytopenia in the patients. This will be carried out utilizing both radioimmunoassays and ELISA techniques for quantitation of IgG and its individual subclasses. In this way we plan on determining whether the amount of type of immunoglobulin present on the cell surface correlates with the extent of immune destruction. The second thrust of the research project will be to utilize the monoclonal antibodies to the immunoglbulin subclasses in specific immunoabsorbent columns in order to isolate the individual sublasses from antisera preparations directed toward the Rh locus (anti-D and anti-CD antisera), antibodies present in the serum of patients with severe autoimmune hemolytic anemia, anti-PLA1 antisera from patients with postransfusion purpura and possibly from the serum of patients with immune thrombocytopenic purpura. These individual immunoglobulin subtype specific antibody reagents will then be utilized to characterize how target cells coated with these specific immunoglobulin subtypes via normal antibody antigen reactions mediate monocyte binding and/or lysis of target cells. We will also carry out studies to determine how one type of immunoglobulin subclass might alter the ability of a second type to mediate monocyte macrophage binding and/or lysis. These studies will thus provide new information as regards the pathogenesis and mechanisms involved in antibody mediated destruction of red cells and platelets.